Fork bottom for motorcycle front suspension

ABSTRACT

A motorcycle whose front end has a coil-over shock disposed within the head tube and telescopic forks which include linear bearings riding between flats on the outer face of the inner fork tubes and flats on the inner face of the outer fork tubes. The linear bearings ride on hardened steel races, enabling the fork tubes to be e.g. aluminum. Using an odd number of linear bearings in each fork prevents having two linear bearings at 180° opposition which would increase sensitivity to manufacturing tolerance stackups, preload, and the like.

RELATED APPLICATIONS

This application is a divisional of co-pending application Ser. No.11/050,377, which was a continuation in part of co-pending applicationSer. Nos. 10/633,381 “Coaxial Steering and Suspension for Motorcycle”and 10/634,041 “Motorcycle Fork Bottom Having Different LongitudinalStiffness and Adjustable Sideways Stiffness” and 10/633,380 “Front EndTrail Adjustment” all filed Jul. 31, 2003 by this inventor, and alsoclaimed benefit of a provisional application 60/632,709 “Linear BearingForks for Motorcycle” filed Dec. 1, 2004 by this inventor.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to suspension components fortwo-wheeled vehicles, and more specifically to front steering and frontspring/shock components.

2. Background Art

The vast majority of motorcycles (and full- and front-suspensionbicycles) are equipped with front suspensions in which a pair oftelescopic forks are coupled to the steering head of the motorcycle'sframe by an upper triple clamp and a lower triple clamp. The tripleclamps provide enough lateral offset that the forks clear the sides ofthe front tire. Trail is a measurement, on the ground, from a pointprojected through the steering axis to the center of the tire's contactpatch directly below the axle, and determines the self-centeringstability of the steering. The triple clamps are usually constructed toprovide some measure of longitudinal offset, as well, to alter thetrail. The forks are either of the conventional “right-side-up” orsliding-female configuration, or the “upside-down” or sliding-maleconfiguration. In either case, a cylindrical tube or piston slidesaxially within a cylindrical cylinder.

In nearly all cases, both the suspension springs and the damping orshock absorbing components are disposed within one or both of thesliding tube assemblies. Unfortunately, because the substantial mass ofthe springs, dampers, oil, and other related suspension components islocated a significant distance—generally in the neighborhood of 2.5inches—from the axis of the steering head, the front end has anundesirably large moment of rotational inertia. In other words, thefront end has a heavy “swing weight” which reduces both the “feel” andthe responsiveness of the front end.

Alternative front end configurations have occasionally been seen, butall suffer from this same malady, and their inventors have beenattempting to solve other problems, such as front end “dive” under hardbraking, rather than reducing the moment of rotational inertia. Examplesinclude the well-known BMW Telelever, the Britten front end, the Hossackfront end, the RADD-Yamaha front end, and various hub-center systemssuch as that found on the Bimota Tesi.

None of these previous geometries places the spring or damper componentscoaxial to the steering head, and all suffer from having stylistic,aesthetic appearances which are dramatically different than the almostuniversally preferred conventional dual fork system. Furthermore, allare significantly more complex than the conventional dual fork system.The downside of these previous systems, such as increased mass, outweighany benefit they may have offered on other fronts.

Some of the more advanced conventional telescopic forks provide externalcontrol knobs for adjusting some, but not all, of the hydraulicdampening characteristics of their internal dampening systems. Forexample, some forks have “clicker” adjusters for altering rebounddampening, compression dampening, and spring preload. There are other,more significant characteristics of conventional forks which are notexternally adjustable, such as spring strength, oil quantity, oilviscosity, shim stacks, and so forth. Furthermore, existing telescopicfork front ends offer front ride height adjustment only by way ofloosening the triple clamps and raising or lowering the upper fork tubeswith respect to the triple clamps. This is a difficult, time consuming,and imprecise operation.

Fork flex, especially under braking, is a significant contributor to thestiction which is known to dramatically reduce the effectiveness andperceived quality of a motorcycle's front suspension.

As a motorcycle rider applies the front brake, the front forks aresubjected to significant flexing force and torque in the direction oftravel, as the rearward force on the front tire's contact patch pressesrearward on the bottom of the forks at the axle, while the inertia ofthe motorcycle's mass presses forward on the top of the forks at thetriple-clamps. Manufacturers battle this flex by using larger-diameterand thus stiffer fork tubes.

Fork flex, especially under braking, is a significant contributor to thestiction which is known to dramatically reduce the effectiveness andperceived quality of a motorcycle's front suspension. The manufacturermay battle this stiction by making even greater increases in thediameter and stiffness of the fork tubes, and by using expensivelycoated bushings, and so forth.

These engineering changes have an unfortunate side effect, which isexposed by the fact that motorcycles lean to the inside when cornering.In general, the faster a corner is taken, the farther over themotorcycle must lean. While leaned over, the axis of the fork suspensionis not perpendicular to the ground, and yet the front tire's contactpatch (which is at the center of the tire when riding straight, but issignificantly off to the side of the tire when the bike is leaned over)remains parallel to the ground. Then, when the front tire encounters abump in the road, the bump forces the tire in the vertical direction,perpendicular to the ground. But, because the forks are not oriented inthat direction, the effect is that the force of the bump is applied tothe forks somewhat laterally (in other words, radially or sideways),rather than axially with respect to the sliding ability of the forktubes.

The forks' stiffness, which the engineer gave the fork tubes tocounteract flex under braking, is now doing exactly the wrong thing withrespect to the force of the bump—it is fighting the bump, rather thansupplely allowing the front tire to track the road surface and remain incontact with the ground. Riders experience this as one form of front endchatter, especially when traversing an extended section of bumpy orrippled racetrack corner. The result is often a front end push which mayend in a crash.

The motorcycle front suspension includes telescopic forks.Traditionally, bushings have been used to reduce friction between theinner fork tube and the outer fork tube. The upper end of the lower tubehas a bushing, and the lower end of the upper tube has a bushing. Undernon-axial loads, such as when braking, the mating surface of the lowerfork tube is levered against the mating surface of the outer fork tube,significantly increasing the friction between the tubes. The shorter thedistance of overlap—that is, the less the inner tube extends into theouter tube—the more pronounced this effect becomes, because the leverarm distance between the upper and lower bushings is reduced. And thegreater the distance between the lowermost point of overlap and theground (where the force is being applied), the greater this effect willbe, because the longer the effective lever arm is.

Bearings provide lower friction than bushings. If the bushings werereplaced with e.g. sets of ball bearings, the friction would besignificantly reduced. However, the ball bearings concentrate theleverage force onto very small areas of the fork tubes, and can causesignificant scoring and gouging of the fork tubes, especially if thefork tubes are made of a material which is not quite hard.

While a ball bearing concentrates its load at essentially a singlepoint, a needle bearing spreads its load over a tremendously increasedarea, in essence a line the length of the bearing. However, while rollerbearings offer the advantage of being able to travel in any direction,needle bearings are limited to traveling back and forth in a singledirection.

Fork tubes are traditionally cylindrical, for a variety of advantageousreasons. Cylinders are relatively easy to machine to consistent and eventolerances. Two cylinders can be mated without any particular clocking(angular) requirements.

Trail is the distance, on the ground, from a point projected through thefront axle on a line parallel with the steering axis, to a pointdirectly below the front axle, or in other words, to the center of thecontact patch. Trail directly impacts the steering stability of themotorcycle and its “return-to-center” force. Trail is affected by rake,which is the angle between vertical and the steering axis; steeper rakereduces trail. Trail is also affected by longitudinal fork offset, orthe distance which the fork tubes are set in front of the frame's headtube; more offset decreases trail. Trail is also affected by axleoffset; if the axle is coupled to the forks in front of their center, itincreases trail.

The rider may wish to increase or decrease trail to, for example, changethe steering feel or feedback, to improve steering quickness, or toeliminate a high-speed wobble, or to reduce a front end “push”. Often,riders will talk as though they are fixing these things by adjusting theride height, which is generally discussed in terms of how far the forksextend up through the top triple clamp. However, decreasing front rideheight by raising the forks farther through the triple clamps in realitysteepens the rake (brings the forks closer to vertical), which, in turn,decreases trail (within the normal adjustment range). It is ultimatelythe change in trail which causes the effects which the rider attributesto his ride height adjustment.

Although adjusting trail can have very beneficial results, the otherchanges which go along with it in a conventional motorcycle may often—oreven usually—outweigh or significantly counteract the benefits of thetrail adjustment. For example, lowering ride height obviously puts theframe, engine cases, fairings, and other parts into closer proximity tothe racetrack, often to an extent that cornering ability is actuallyreduced because hard parts of the motorcycle ground out on curbings oreven the asphalt itself; it also changes the weight transfer bias underbraking.

What is needed, then, is a system which has the aesthetic appeal andsimplicity of the dual fork geometry, with a significantly reducedmoment of rotational inertia. What is further needed is a system whichoffers reduced stiction.

What is also needed, then is an improved front fork which has suitablylow lateral stiffness to better enable the front tire to track groundirregularities while leaned over cornering, without compromising itsexcellent longitudinal stiffness to resist flexing under hard braking.What is further desirable is such a fork which has adjustable lateralstiffness.

What is further needed is a mechanism which facilitates trailadjustments without adversely affecting other geometry of the motorcyclesuch as ride height and rake angle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood more fully from the detaileddescription given below and from the accompanying drawings ofembodiments of the invention which, however, should not be taken tolimit the invention to the specific embodiments described, but are forexplanation and understanding only.

FIGS. 1-4 show various views of one embodiment of the front end andsteering/suspension system of the present invention.

FIG. 5 shows an exploded view of the steering/suspension system.

FIG. 6 shows a perspective, cutaway view of a portion of thesteering/suspension system.

FIG. 7 shows a motorcycle having the coaxial steering and suspensionfront end of this invention.

FIG. 8 shows one embodiment of a fork according to this invention.

FIG. 9 shows a more detailed exploded view of some of the components ofone embodiment of a fork bottom according to this invention.

FIG. 10 shows a different angle view of the fork bottom, particularlypointing out the attachment points for the flex control mechanism.

FIG. 11 shows another embodiment of a fork bottom which has differentlateral and longitudinal stiffness.

FIG. 12 shows a motorcycle front end equipped with linear bearings,according to another embodiment of this invention.

FIG. 13 shows an exploded view of a portion of the front end of FIG. 12.

FIG. 14 shows a partially cross-sectioned view of a telescopic forkequipped with linear bearings.

FIGS. 15 and 16 show top or axial views of a linear bearing telescopicfork having six and five sets of linear bearings, respectively

FIGS. 17-20 show one embodiment of a motorcycle front end having a shockmounting system according to another embodiment of this invention,demonstrating removal of the shock facilitated by rotation of thebracket which engages with the fork bridge, without requiringdisassembly of the telescopic forks nor loosening of the triple clamps.

FIGS. 21-23 show the telescopic fork in a compressed, middle, andextended position, respectively, particularly showing relative motion ofthe linear bearings to the inner and outer fork tubes.

FIG. 24 shows another embodiment of a linear bearing fork tube having aspring-loaded bearing follower for keeping the linear bearings fromratcheting or wandering out of position.

FIG. 25 shows another embodiment in which a bearing stop prevents thelinear bearings from ratcheting or wandering out of position.

FIGS. 26-28 show the fork bottom equipped with different trailadjustment blocks.

FIG. 29 shows the mating features of the trail adjustment block and thefork bottom.

FIG. 30 is a partially cross-sectioned view of one embodiment of a forklower, showing its mating with a trail adjustment block, including adetail view.

FIG. 31 is a partially cross-sectioned view of another embodiment of afork lower, showing its mating with another trail adjustment block,including a detail view.

FIG. 32 shows another embodiment of a gusseted fork bottom.

DETAILED DESCRIPTION Coaxial Steering and Suspension Components

FIGS. 1-4 illustrates one embodiment of a motorcycle front end 10 andspecifically the steering/suspension system 50, viewed generally fromthe front in FIGS. 1 and 2, the left side in FIG. 3, and the rear inFIG. 4. The front end includes a tire 12 mounted on a wheel 14 andequipped with brake rotors 16 and brake calipers 18. A fork bottom 20includes a fork bottom body coupled to the axle 22 and to a pair of malelower fork tubes 24 which slide in a pair of female upper fork tubes 26.In other embodiments, conventional fork tubes are used, without forkbottoms. A lower triple clamp 28 and an upper triple clamp 30 arecoupled to the upper fork tubes and couple them to a steering stemassembly (not visible) which rotates within a head tube 32 which is partof, or coupled to, the frame (not shown) of the motorcycle.

The front end 10 thus pivots or rotates about a steering axis which iscoaxial with the head tube 32. This invention differs from the prior artin that at least one of the spring (suspension) and/or shock (damping)components is coaxially disposed within the head tube. In oneembodiment, a single coil-over shock 34 provides both spring support anddamping for the front end, while in other embodiments, a moreconventional cartridge system (not shown) could be employed within thefork tubes. The bottom end of the coil-over shock is coupled to a forkbuttress 36. The fork buttress may be coupled to the lower fork tubes orto the fork bottoms. In one embodiment, the fork buttress comprises twohalves, each of which is integrally formed with a respective forkbottom, as shown.

FIG. 5 illustrates the steering/suspension system 50 of the motorcyclefront end, viewed generally from the front and shown in an explodedview. For ease of illustration, only a single fork will be described.The upper fork tube 26 threads or, preferably, clamps into the uppertriple clamp 30. A fork cap 52 seals the open end of the fork tube toprevent contamination of the sliding components, but is not necessarilyan airtight seal. A stationary fork bushing 54 and a seal 56 fit withinthe lower end 48 of the upper fork tube, and are held in place by a snapwire 58. A sliding fork bushing 60 mates with the upper end 62 of thelower fork tube 24. The stationary and sliding fork bushings provide alow-stiction but tight-tolerance sliding fit of the lower fork tubewithin the upper fork tube. In practice, the components may need to beassembled in a slightly different manner than suggested by this explodedview, as the bushings are not generally able to slide past each other,and their interference is part of what keeps the telescopic forks fromtelescoping completely to disassembly.

A steering tube 66 rotates within the head tube 32 on an upper bearing68 and a lower bearing 70. A jam nut 72 and washer 74 secure the upperbearing onto the steering tube. A top bolt 76 threads into the steeringtube and secures it to the upper triple clamp.

The lower end 78 of the lower fork tube threads or otherwise couples toa hole 80 in the upper end 42 of the fork bottom 20. The upper end ofthe coil-over shock 34 fits up into and engages the steering tube, whilethe lower end of the monoshock engages the fork buttress 36 at the upperend 42 of the fork bottom.

The lateral stiffness of the fork bottom is controlled by a tensioncable or rod 82. In some embodiments, the tension rod may apply tensionor pull. The lower end 84 of the tension cable engages the fork bottom,while the upper end 86 of the tension cable is engaged and tensioned bya tension adjuster 88. The tension adjuster and a washer 90 engage atension adjuster block 92 which fits into a hole 94 in the upper end ofthe fork bottom. A detent ball 96 retains the tension adjuster withinthe tension adjuster block and, in some embodiments, provides “clicker”adjustment feedback as is commonly present in other motorcyclesuspension adjustments such as compression and rebound damping. Foraesthetics and aerodynamics, a fork bottom inner cover 98 may be coupledto the inward-facing portion of the fork bottom, covering the tensioncable and other components.

FIG. 6 illustrates further details of one embodiment of thesteering/suspension system 50, with a cutaway for visibility into thecoaxial alignment of the suspension components within the head tube 32.The suspension components are illustrated somewhat generically and in amuch simplified configuration omitting many details which are notessential to understanding this invention but which are well within theabilities of those of ordinary skill in the art. The suspensioncomponents may include one or more load-bearing components such as acoil spring 110, and one or more damping components 112. As such, thesuspension components may be quite similar to a conventional rear shocksuch as is conventionally used in modern sportbikes, with the additionof a suitable mounting mechanism 114 adapted for coupling or mating withthe fork brace (not shown) or other lower mounting component.

The suspension components are disposed coaxially with the head tube 32,or, more precisely, coaxially with the steering axis. The steering tube66 is disposed coaxially within the head tube, and rides on an upperbearing 68 and a lower bearing 70. The jam nut 72 is threaded onto thesteering tube. The top bolt 76 threads into the steering tube andcoaxially locates the upper triple clamp 30 with respect to the steeringaxis. The top bolt is provided with, in one embodiment, an internal hexsocket 116 by which the top nut is tightened.

In one embodiment, the top nut is further provided with a passage 118and the steering tube is provided with a passage, through which a tool(not shown) can be inserted to adjust various settings of the suspensioncomponents, such as compression damping, rebound damping, preload, rideheight, and so forth. Again, for ease of illustration, these variousadjustment mechanisms are not shown on the coil-over shock.

One noteworthy feature of this system is that the ride height of thefront end can be adjusted by screwing threaded rod 120 up and down inthe steering tube, and this is completely independent of the coupling ofthe forks to the triple clamps. This represents a marked improvementover the conventional fork systems, in which the rider must loosen theupper and lower triple clamps, slide or pound the upper fork tubes upand down in the triple clamps until a desired amount of protrusion isachieved, then retighten the triple clamps, while hoping that the forktubes have not shifted and that the two fork tubes are set at exactlythe same height. The coaxial monoshock adjustment of this inventionenables the rider to adjust the ride height without fiddling with thetriple clamps or fork tubes, and it guarantees a single, consistentsetting without the possibility of maladjustment between the two forks.The same monoshock principle applies to other adjustments, as well, suchas compression damping, rebound damping, and so forth.

FIG. 7 illustrates a motorcycle 150 having a front end 50 with thecoaxial steering/suspension system of this invention.

Forks Having Flexible Fork Bottoms

FIG. 1 illustrates a fork bottom 20 including a fork bottom body coupledto the axle 22 and to the lower fork tubes 24. The longitudinal (in thedirection of travel) stiffness of the fork bottom is different than thelateral (side-to-side) stiffness of the fork bottom. In one embodiment,the longitudinal stiffness is greater than the lateral stiffness. Insome embodiments, the lateral stiffness of the fork bottom isadjustable, as explained below.

FIG. 8 illustrates one embodiment of a fork 40 according to thisinvention. The fork includes an upper fork tube 26, a lower fork tube24, and a fork bottom 20. The fork bottom includes a sturdy upper end 42adapted for receiving and retaining the lower fork tube by any suitablemeans such as pinch bolts (not shown), threads (not shown), or the like.In one embodiment, the fork's half buttress 36 is integrally formed withthe sturdy upper end of the fork bottom. The fork bottom furtherincludes a lower end 44 adapted f6r receiving and retaining the axleassembly (not shown) and the brake caliper (not shown) by any suitablemeans. The upper fork tube includes an upper end 46 adapted for beingsecured to the upper triple clamp (not shown) by any suitable means,such as threads (not shown) or pinch bolts (not shown). The upper forktube includes a lower end 48 adapted for providing a good sliding fitwith the lower fork tube.

In some embodiments, especially those in which both the spring and shockcomponents are located coaxially within the head tube, the forks can bemuch simplified versus the prior art. For example, the telescoping forktubes do not need to be made to have a fluid-tight seal, as there is noneed for them to retain the oil which would be used in a damping system.In fact, in some embodiments, it will be found desirable to ventilatethe upper fork tube, the lower fork tube, and/or the fork bottom, toeliminate any pressurization caused by the pumping action of the forksas they extend and compress.

FIG. 9 illustrates further details of one embodiment of the adjustableflex fork bottom assembly 100. The left fork bottom 20 is shown, asviewed from the front and right, or generally where the front of thetire would be. The side wall 102 of the fork bottom provides stiffnessin the longitudinal direction, the direction of travel and braking,while the fact that the fork bottom is not a complete cylinder gives ita measure of lateral flex, from side to side.

A gusset 104 near the middle of the fork bottom provides a fulcrum overwhich the tension cable 82 is stretched, and may be provided with one ormore grooves 106 or bearings or other means for holding the tensioncable in a desired position. The lower end 84 of the tension cable isprovided with a ball or other means for coupling to the lower end of thefork bottom. The upper end of the tension cable is provided with athreaded rod 86 which engages threads on the tension adjuster 88. Thetension adjuster may be provided with a hexagonal socket 108 by which amechanic can set the flex by tightening or loosening the tension cable,and thus the lateral pressure on the fulcrum 104, thereby changing theamount of lateral flex of the fork bottom. In other embodiments, otheradjustment mechanisms may be employed, such as a cammed lever.

As the tension on the tension cable is increased, the fork bottom isplaced under increased lateral tension as the tension cable presses downharder and harder on the fulcrum. This tends to make the fork bottomless flexible in the side-to-side dimension, while having little effecton its stiffness in the longitudinal direction. Thus, the inventionenables the rider to set up his front suspension to be more or lesscompliant in lateral flex, to tune the suspension for the mid-comerbumpiness or smoothness of a particular road or racetrack, withoutcompromising longitudinal stiffness which provides good control underheavy braking and which helps eliminate stiction in the telescopic forktubes. In some cases, the rider may even choose to adjust one fork'ssideways flex differently than the other's.

The skilled suspension engineer will be able to select materials,thicknesses, and geometries to provide the desired longitudinal andlateral stiffnesses for his application at hand. For example, in oneembodiment, the entire fork bottom is constructed as a monolithic metalstructure, such as of cast aluminum. In another embodiment, the centralportion of the fork bottom may be fashioned of carbon fiber, while theupper and lower ends may be fashioned of titanium.

FIG. 10 illustrates the left fork bottom 20 in further detail, viewedfrom the front and below, to better demonstrate the mounting of thetension cable (not shown). The upper end of the tension cable is fedthrough a hole 1 10 in the lower end of the fork bottom and pulledthrough until the ball (at the lower end 84 of the cable) engages thehole 110. The cable is routed through the groove 106 on the fulcrum 104and through a hole 112 in the upper end of the fork bottom, then thetension adjuster (not shown) is engaged with the tension cable to placeit under tension and retain it.

In other embodiments, alternative mechanisms could be used instead ofthe tension cable. For example, a pair of threaded rods could eachengage the fulcrum and a respective end of the fork bottom, and the rodscould be used to place the fork bottom under tension or even underelongating pressure, and the rods could operate independently in somemodes. Or, the tension adjustment could be made at the fulcrum, ratherthan at the end of the tension cable, such as via a jack screw. Inanother embodiment, the adjustable tension cable could be replaced by aset of alternative vertical inserts placed inside the fork bottom toprovide various amounts of end-to-end pressure or tension. Such insertswould advantageously be placed generally perpendicular to the side walland fulcrum shown in these drawings.

FIG. 11 illustrates another embodiment of a fork bottom 121 which has adifferent stiffness in the longitudinal direction than in the lateraldirection. Shown is a right fork bottom, seen from the front and left.The fork bottom includes an upper end 122 adapted with a hole 124 forreceiving the lower fork tube (not shown), and a lower end 126 adaptedwith a hole 128 for receiving the axle (not shown). A slot 130 and apinch bolt hole 132 are provided for retaining the axle by a pinch bolt(not shown). The middle portion 134 of the fork bottom includes a sidewall 136 which provides good longitudinal stiffness. A series of slits138 soften the central portion of the fork bottom, giving it moreflexibility in the lateral direction. The slits may be provided withholes 140 at their terminal ends, to prevent the slits from tearing orspreading further through the material of the fork bottom. As the forkbottom flexes toward the side such that the slits compress, at the pointat which the sides of the slits meet, the fork bottom will become morerigid. In some embodiments, the slits may be made of differentdimensions (e.g. vertical height in the orientation shown), such thatthey do not all pinch closed at the same amount of lateral flex, for amore “progressive” and less abrupt increase in the lateral stiffness ofthe fork bottom.

FIG. 7 illustrates a motorcycle 150 adapted with the front end havingthe forks of the present invention, including upper fork tubes and lowerfork tubes, and including fork bottoms having different longitudinalstiffness and lateral stiffness, and having adjustable lateralstiffness.

Telescopic Fork Tubes Having Linear Bearing

FIG. 12 illustrates a motorcycle front end 160 similar to that of FIG.1, which has been further improved to further reduce stiction. Thetelescopic forks 162 ride on linear bearings (not shown) rather than onbushings. A single-piece fork bridge 164 or buttress couples the lowerends of the forks together and to their respective fork bottoms 166.

FIG. 13 illustrates an exploded view of various components of themotorcycle front end 160. The right fork (shown on the left in thisfront view) is shown in a slightly more exploded state than the leftfork. Outer fork tubes 168 have “flats” 170 extending axially alongtheir inner surfaces, and inner fork tubes 172 have flats 174 extendingaxially along their outer surfaces. Sets of linear bearings 176 aredisposed between corresponding flats of the inner and outer fork tubes.In one embodiment, hardened outer bearing races 178 are disposed withinor upon the flats of the outer fork tubes and hardened inner bearingraces 180 are disposed within or upon the flats of the inner fork tubes,and the linear bearings contact the races rather than the fork tubesthemselves. This permits the fork tubes to be made of light weightmaterials such as aluminum, which might be damaged if the bearings—whichare typically made of harder materials such as steel—were to directlycontact the fork tubes.

In one embodiment, each linear bearing includes a plurality of needlebearings held in a strip-shaped cage. In other embodiments, otherbearing configurations may be employed, such as ball bearings. Needlebearings are, however, preferred, because they spread the bearing loadsover a larger surface area than e.g. ball bearings.

An upper triple clamp 182 and a lower triple clamp 184 are coupled tothe upper fork tubes. In one embodiment, the upper fork tubes areclocked (or, in other words, rotationally oriented) to one or both ofthe triple clamps, to provide symmetrical bearing loading between theleft fork and the right fork, as well as to provide a clean, symmetricalcosmetic appearance. Fork caps 186 secure the upper fork tubes to theupper triple clamp, such as by threading into the upper fork tubes andpinching onto the upper triple clamp. Optionally, dust seals 188 arefitted to the lower ends of the upper fork tubes, to reduce the amountof dust, grit, and other contaminants which enter the fork tubes, toextend the life of the linear bearings and to maintain a smooth,notchless telescopic feel.

A head tube 190 is coupled to the frame (not shown). A steering tube 192is disposed within the head tube and rides on an upper bearing 194 and alower bearing 196. A coil-over shock 198 is disposed within the steeringtube. The shock's upper end is coupled to the steering tube or to theupper triple clamp, and the shock's lower end is coupled to the forkbridge.

FIG. 14 illustrates a portion of a linear bearing telescopic fork 200according to one embodiment of this invention. The telescopic forkincludes an outer fork tube 168 which includes a plurality of flats 170disposed about its inner diameter. Hardened races 178 are disposedwithin or upon those flats, and are shown in partially truncated viewfor better visibility of the distinction between the flat and the race.An inner fork tube 172 is disposed within the outer fork tube andincludes a plurality of flats 174 which are disposed about its outerdiameter so as to be adjacent and substantially parallel withcorresponding flats of the outer fork tube. Hardened races 180 aredisposed within or upon these flats, and are shown in partiallytruncated view for better visibility of the flats and races. Linearbearings 176 are disposed between opposing races or flats. For clarity,the inner race has been omitted from one of the inner tube's flats 175,some of the bearings have been omitted, and some of the outer races havebeen omitted. A dust seal 188 is coupled to the end of the outer forktube which overlaps the inner fork tube. In some embodiments, anold-school “right-side-up” fork configuration could be used, with theinner fork tube being coupled to the triple clamps and the outer forktube being telescopically extendible and coupled to the front axle. Butin the preferred embodiment, an “upside-down” fork configuration isused, as illustrated.

FIG. 15 illustrates an axial view of one embodiment of a telescopic fork200, showing the outer fork tube 168 with its flats 170 and races 178,and the inner fork tube 172 with its flats 174 and races 180. Linearbearings 176 are disposed within opposing inner and outer races. In oneembodiment, there are an even number of bearing sets, such as six.

FIG. 16 illustrates an axial view of another embodiment of a telescopicfork 210 in which there are an odd number of bearing sets 176, such asfive. In the embodiment shown in FIG. 15, there are pairs of opposedbearing sets which are disposed at 180° spacing around the axis of thefork. That configuration can in some instances cause increasedsensitivity to manufacturing tolerance stackups, leading to difficultyin keeping equal preload on all bearing sets.

It has been found that, by using an odd number of bearings as shown inFIG. 16, the tolerance and preload problems are significantly reduced.The number of bearings can be selected according to the needs of theparticular application at hand. In some cases, three may be adequate. Insome cases, seven or more may be desirable. However, the preferredembodiment for use in the roadracing motorcycle of applicant's intendedusage is to use five sets of bearings. Note that a “set” may includemore than one cage of bearings in the same race channel.

The clocking or orientation of the bearings, whether an odd number or aneven number, can in some cases also affect the performance of the forks.The heaviest loads that the bearings experience will generally be underfairly straight-line braking. Referring also to FIGS. 7 and 12, it willbe understood that, under heavy braking, the road contact patch appliesrearward force to the tire, which tends to drive the rearmost portion orside of the lower, inner fork tube against the rearmost lower portion orside of the upper, outer fork tube. This region acts then as a fulcrum,and the lower, inner fork tube levers over this fulcrum such that thefrontmost portion or side of the upper end of the lower, inner fork tubeis driven against the frontmost portion or side of the upper, outer forktube.

It has been found desirable to clock the fork tubes with respect to thelongitudinal axis of the motorcycle such that each fork is laterallysymmetrical, such as shown in FIGS. 15 and 16 (in which it is assumedthat the front of the motorcycle is facing e.g. the bottom of the page).In some embodiments, it is desirable that a bearing set be clocked atthe frontmost position of the forks.

A needle bearing applied to roll axially up and down a cylindrical forktube would lose the main advantage of the needle bearing, in that itsload would be concentrated at the point where the cylindrical fork tubeis tangent to and in direct contact with the needle bearing.

However, if flats are machined into the fork tube, the needle bearingcan spread its load over its entire length.

If the fork tube is made of a soft material, such as light weightaluminum, even a needle bearing may not be sufficient to preventeventual damage of the fork tube. If hardened steel races are placed inthe flats, the needle bearing rides on the races and does not contactthe fork tube. If corresponding flats are machined into the inner andouter fork tubes, the needle bearing does not touch either fork tube.

The fork tube can initially be fabricated as a cylinder, formanufacturing and tolerance purposes. The flats can then be machined inwhere needed. Advantageously, the flats can be machined in sufficientlyfar that the races do not extend outwardly beyond the original materialof the cylinder; that is, the flats should be machined in at least asdeep as the races are thick.

If the flats are machined in such that the elongated edges of the flatsare somewhat under-cut, the flats can be slid in from one end, andcannot fall out radially. A screw or other means can be provided toprevent the races from sliding out axially.

As the inner fork tube moves in and out of the outer fork tube a givendistance, the needle bearing moves half that distance. It rollsrelatively up one tube, and relatively down the other tube. However, dueto friction, vibration, and other factors, this does not mean that, overan extended period of operation, the needle bearing will return toexactly the same starting point. Over time, the needle bearing may tendto wander toward one end of the assembly. This is true even if there issome degree of initial preload in the assembly. Preload means that thenominal or theoretical space between the opposing flats (or races) ofthe inner and outer tubes is slightly smaller than the actual diameterof the needle bearing, and that the materials of the tubes and/orbearing are deformed under compression or tension upon assembly. Preloadis desirable, to reduce “slop” in the assembly, but may contribute toincreased wear and the like.

A plurality of needle bearings can be held in position relative to oneanother by a linear bearing cage. Such an assembly can simply bereferred to as a linear bearing. The linear bearing should be longenough to provide adequate support for the overlapping, telescoping forktubes.

It is advantageous to have an odd number of flats in each fork tube. Ifthere were an even number, e.g. six, then there would be opposing pairse.g. one and four, two and five, three and six. These opposing pairsincrease the difficulty of assembly, increase wear of the assembly, andsignificantly increase the undesirable effects of preload such as thefeel of notchiness which occurs in many kinds of bearings (includingroller bearings) when they are overly preloaded or overly tightened.They also increase the bad effects of machining tolerance variations. Inone embodiment, five flats and five corresponding sets of linearbearings has been found to be an excellent telescopic fork.

Having an inner fork tube whose outer surface is not purely cylindrical,significantly complicates such things as sealing the fork tube assembly.Conventional cylindrical oil seals are inadequate to keep the forks fromleaking badly. However, if the fork tubes are merely telescopic sliders,and the hydraulic dampening mechanism is not located within the forktubes (or is a self-sealed cartridge style assembly), there is noproblem. The linear bearing fork tubes are especially well-suited foruse in combination with applicant's co-pending invention which moves thehydraulics into the steering stem, leaving the forks to provide onlytelescopic movement. The springs could still be located in the forktubes, or a spring could be in the steering stem.

Quick-Change Coaxial Front Shock

FIGS. 17-20 illustrate another embodiment of a motorcycle front end 220in which a single coil-over shock 198 is disposed coaxially within thehead tube 190. The top end of the shock is coupled to the upper tripleclaim 182 or to the steering tube (192, not visible), and the bottom endof the shock includes a bracket 222 which is coupled to a generallyplanar surface 224 of the fork bridge 164.

To rapidly swap out the shock, in order to replace it with another shockhaving different spring or damping parameters (e.g. stiffer spring,different oil, different shim stack, etc.), bolts (not shown) areremoved from the mounting holes 226, and the bracket is rotated (FIG.18) until it clears the fork brace (FIG. 19), then the shock can bethreaded out of the steering tube. The replacement shock is inserted byreversing this process. In some embodiments, the surface 224 is recessedinto the fork brace. In some embodiments, the front of the surface 224has a curved edge 228 whose radius substantially matches a radiusthrough which an outermost edge of the bracket swings as the shock isrotated.

Linear Bearing Retention

FIGS. 21-23 illustrate the telescopic action of the linear bearing fork200. As the fork extends, with the inner fork tube 172 extending furtherand further out of the outer fork tube 168, the linear bearings 176travel in that same direction but at half the speed and half thedistance.

It is desirable, then, that the linear bearings have a length and aposition such that they provide sufficient bearing surface area couplingthe inner and outer fork tubes, throughout the range of travel of thefork tubes. In some embodiments, this will mean that the linear bearingsshould at all positions be fully engaged with the inner fork tube. Inother embodiments, it may be acceptable for the linear bearings topartially extend beyond the inside end of the inner fork tube near fulltelescopic extension. In some embodiments, it may be desirable that thelinear bearings never extend out of the overlapping end of the outerfork tube, while in other embodiments it may be acceptable if theyprotrude somewhat at full extension.

The length and positioning of the linear bearings can readily bedetermined by the skilled mechanic upon assembly of the fork, dependingupon the particular demands of the application at hand.

In some applications, the linear bearings may tend to ratchet or wanderover time, such that they do not always return to the same axialposition when the forks are returned to the same telescopic position.This is in some measure dependent upon the preload, in some measuredependent upon the materials and strength of the fork tubes, and soforth. In some embodiments, it may be desirable to prevent suchratcheting or wandering.

FIG. 24 illustrates a linear bearing telescopic fork 230 which includesan inner fork tube 172 and an outer fork tube 168 and a plurality oflinear bearings 176. A bearing follower 232 is disposed within the outerfork tube above the inner fork tube so as to be in contact with theupper ends of any linear bearings which ratchet far enough to extendbeyond the upper end of the inner fork tube. The ratcheting is shown ina highly exaggerated fashion here, to illustrate the point. The followerprovides axial pressure on the over-extending ends of the linearbearings, helping them to stay in position. In some embodiments, theweight of the follower is sufficient to accomplish this purpose. Inother embodiments, a spring 234 or other device is used to providepressure. The spring can be coupled to the inner fork tube, as shown, orit could be on the upper side of the follower and coupled to the outerfork tube or to the fork cap (not shown).

FIG. 25 illustrates another embodiment in which, rather than a follower,a simple stop 236 is employed. This is a less desirable embodiment,because the stop will only encounter the bearing at the bearing's mostupward point of travel with respect to the outer fork tube, which is thebearing's most downward point of travel relative to the inner fork tube.In some embodiments, the stop can be placed farther down the outer tube,such that its lower edge is at the highest point that the bearing shouldtravel; in the figure, it is shown at an extremely high position simplyso that it is visible.

Axle Mounting Block Retention

FIGS. 26-28 illustrate the front end with three different trail blocksinstalled, producing three different amounts of trail. In FIG. 26, thefork bottom 20 is equipped with a first trail adjustment block 240Awhich provides a first amount of trail. For the sake of convenience, thetrail is represented simplistically as it is related to the distancefrom the axial center of the front axle to the back of the trailadjustment block, rather than as a distance on the ground, but thereader will readily appreciate that the two are interrelated (becausethe front tire contact patch is behind the projected steering axis pointon the ground, moving the front axle forward decreases trail, eventhough FIGS. 26-28 express a distance between the axle and a point onthe fork bottom which increases as the axle is moved forward) (becausethe contact patch is behind the projected steering axis point on theground). In the instance of FIG. 26, the trail block offset is 1.37inches, corresponding to 4.0 inches of trail. The brake caliper 242 ismounted to the fork with a set of first caliper spacers 244A, which aresized to provide a particular distance from the center of the front axleto the brake pads (not shown). In FIG. 27, the fork bottom 20 isequipped with a second trail adjustment block 240B with a trail blockoffset of 1.58 inches, corresponding to 3.75 inches of trail. The brakecaliper 242 is mounted with a set of second caliper spacers 244B whichare sized to provide the same distance from the center of the frontaxle, which has been moved forward relative to its position in FIG. 26,to the brake pads, so the brake pads maintain the same relative positionwith respect to the brake rotors (not shown, but which will have movedforward along with the front axle). In FIG. 28, the fork bottom 20 isequipped with a third trail adjustment block 240C with a trail blockoffset of 1.83 inches, corresponding to 3.5 inches of trail, and thebrake caliper is mounted without a spacer to keep the same distance fromthe axle to the brake pads.

It should again be noted that, in one embodiment, the trail adjustmentblocks and their mating surface of the fork lower are configured suchthat the front axle is moved, by the various trail adjustment blocks, ina direction parallel to the ground, such that the front ride height isnot changed by swapping out the different trail adjustment blocks. Inone embodiment, this is accomplished by providing the trail adjustmentblock with a top surface and a bottom surface which are parallel, and bypositioning the front axle hole at various positions, for the varioustrail adjustment blocks, which are a same distance from the bottomsurface, for example. In other embodiments, other geometries mayaccomplish the same result.

The trail adjustment block may be tightened onto the axle, and the forklower may be tightened onto the trail adjustment block, by one or morepinch bolts (not shown) which may advantageously be inserted upwardthrough the bottom end of the fork lower through coaxial holes (notshown) through the portion of the fork lower which is below the trailadjustment block, the portion of the trail adjustment block which isbelow the pinch split, the portion of the trail adjustment block whichis above the pinch split, and the portion of the fork lower which isabove the trail adjustment block. In this instance, only the topmost ortwo topmost of these need to be threaded.

In one embodiment, the brake caliper is mounted not only “radially”, butalso with its radius parallel to the plane in which the various trailadjustment blocks move the front axle, to maintain a constantpositioning of the brake pads and the brake rotor across the varioustrail settings. In one embodiment, the radius of the brake caliper mountis parallel to the ground.

FIG. 29 illustrates further details of the trail adjustment block 240and the lower end of the fork bottom 20, specifically illustrating onemechanism by which axial alignment can be achieved. The fork bottom isillustrated in a truncated fashion, for simplicity. The trail adjustmentblock includes a top surface 246 and a parallel bottom surface (notvisible) which, respectively, mate with a top surface (not visible) anda parallel bottom surface 248 of the fork. The back surface 250 of thetrail adjustment block mates with a back surface 252 of the fork lower.These matings provide up-and-down and forward-backward alignment of thetrail adjustment block with respect to the fork lower. In oneembodiment, in order to provide positive and consistent lateralalignment (with respect to the front axle, not shown, but centered inthe axle mounting hole 254), the upper and lower surfaces of the trailadjustment block are adapted with parallel grooves 256 which mate withcorresponding parallel ridges 258 on the lower and upper surfaces of thereceiving recess of the fork bottom. Other embodiments are certainlyviable, such as swapping the grooves and the ridges, or one of each, orby using mounting pins and holes, or simply by using the correspondingpinch bolt holes 260, 262 and the pinch bolt (not shown).

The ridge-and-groove arrangement prevents the trail adjust block frommoving axially with respect to the front axle.

FIG. 30 illustrates this arrangement in partial cross-section view, withonly the trail adjust block and the ridge cross-sectioned, to illustratetheir engagement. The left and right shoulders of the fork bottom'smating ridges 258 engage with corresponding left and right shoulders ofthe trail adjust block's grooves 256.

FIG. 31 illustrates another, simpler embodiment. Because the front wheeland axle spacers (not shown) prevent significant inward movement of thetrail adjust block 272, all the fork bottom 270 needs to do is toprevent the trail adjust block from slipping axially outward orlongitudinally forward. The fork bottom includes a ridge 274 whichincludes a shoulder at its inward edge, and the trail adjust blockincludes a ridge 276 which includes a shoulder at its outward edge.These shoulders engage and prevent the trail adjust block from slippingoutward. A pinch bolt hole 278 can be used to retain the trail adjustblock, preventing longitudinally forward movement relative to the forkbottom. This simplifies the machining of the fork bottom and trailadjust block.

Gusseted Fork Bottom

FIG. 32 illustrates another embodiment of a fork bottom 270 whichincludes an elongated C-beam cross-sectional shape for high longitudinalrigidity with some measure of lateral flexibility. The inner face of thefork lower has been beefed up with a plurality of cross-webbed gussets272. The thickness and lateral depth of the gussets impacts both thelateral and longitudinal stiffness, and can be selected according to theneeds of the application at hand.

Conclusion

The reader will readily appreciate that having the suspension componentsmounted coaxially with the steering head provides several significantadvantages. For example: the moment of rotational inertia of the frontend is reduced, versus that of a conventional front end in which thesuspension components are located out in the fork tubes; only a singleset of suspension components is required, and yet the suspension has thesame affect at each side of the front axle, whereas putting a single setof components in e.g. only the left fork of a conventional front endwould produce disastrous results; preload, rebound damping, compressiondamping, and ride height adjustments can be made with a singleadjustment each, versus the two adjustments each that are required in aconventional front end, and can be done without loosening the forks inthe triple clamps; suspension settings cannot accidentally be differenton the two sides of the front end, whereas this is a constant dangerwith a conventional front end; stiction is reduced; and yet the familiarand desirable look and feel of a conventional dual fork front end areretained. Furthermore, it may often be the case that the total mass ofthe required suspension is lower when using the present invention, thanwhen using a conventional front end.

While the invention has been described with reference to its use in amotorcycle, the invention is not limited to motorcycles, but can be usedin bicycles, automobiles, and other vehicles. And while the inventionhas been shown as using an “upside-down” fork, it may alternatively beused with a “right-side-up” fork. Some components have been illustratedas being of monolithic construction, while other components have beenillustrated as being separate components coupled together. The readerwill readily appreciate that the designer may elect, within the scope ofthis invention, to split some components into separate sub-components,or to combine various components into a monolithic whole. The readerwill further appreciate that the invention may be practiced in a“single-sided” front end, such as that found on some bicycles which haveonly a single fork. The term “triple clamp” should not necessarily beinterpreted to mean that two forks are required with the steering tube.The presence of one or more suspension components coaxial with thesteering axis does not necessarily prohibit the additional presence ofone or more suspension components elsewhere, such as within the forks.

The sliding-tube forks may be empty, containing neither springs nordampers, and may thus be said to have substantially inert suspensioncharacteristics. In some embodiments, the suspension components could belocated externally to the outer steering tube, rather than inside it.

While it might, at first glance, be assumed to be a negative that thehead tube must, in the present invention, be significantly larger thanin a conventional front end, the opposite is actually true. Having avery large diameter head tube, with very large diameter bearings and soforth, reduces frame torque and makes the frame stronger, especially atthe points at which the rest of the frame joins the head tube.

While the invention has been described with reference to its use in amotorcycle, the invention is not limited to motorcycles, but can be usedin bicycles, automobiles, and other vehicles. And while the inventionhas been shown as using an “upside-down” fork, it may alternatively beused with a “right-side-up” fork. Some components have been illustratedas being of monolithic construction, while other components have beenillustrated as being separate components coupled together. The readerwill readily appreciate that the designer may elect, within the scope ofthis invention, to split some components into separate sub-components,or to combine various components into a monolithic whole. For example,the lower fork tube and the fork bottom could be formed as one integralcomponent. The fork bottom has been shown having a length such that itextends to or above the top of the front tire, but the invention is notthus limited; rather, any suitable length fork bottom may be used, solong as it has meaningfully different stiffness in the longitudinal andlateral directions (in contrast to the small mounting structures,typically machined from billet, which are found on the bottom ofconventional upside-down forks).

The reader will further appreciate that the invention may be practicedin a suspension having only a single fork, and that the “triple clamps”will not in that case have means for coupling a third tube, but only thehead tube and the upper fork tube.

The fork and the trail adjustment block have been illustrated in aconfiguration in which the trail adjustment block slips into the frontof the fork. In other embodiments, a different mating system could beemployed. For example, instead of an indentation or receptacle formedinto the front of the fork, the fork could have a hole extendinglaterally through it, or, in other words, there could be fork materialin front of the receptacle, and the trail adjustment block would beinserted laterally rather than longitudinally. Alternatively, thereceptacle could be oriented generally downward, such that the forkbottom is lowered onto the trail adjustment block.

When one component is said to be “adjacent” another component, it shouldnot be interpreted to mean that there is absolutely nothing between thetwo components, only that they are in the order indicated. The variousfeatures illustrated in the figures may be combined in many ways, andshould not be interpreted as though limited to the specific embodimentsin which they were explained and shown. Those skilled in the art havingthe benefit of this disclosure will appreciate that many othervariations from the foregoing description and drawings may be madewithin the scope of the present invention. Indeed, the invention is notlimited to the details described above. Rather, it is the followingclaims including any amendments thereto that define the scope of theinvention.

1. A fork bottom for coupling a motorcycle's telescopic front fork to a front wheel's axle, the fork bottom comprising: a body at least six inches tall and having a cross-sectional shape giving the body greater longitudinal stiffness than lateral stiffness; a receptacle substantially at the body's lower end, the receptacle having a ridge with a shoulder on an inwardmost side toward the wheel; an axle positioning block having an outer surface shaped to fit within the receptacle, the outer surface having a ridge with a shoulder on an outwardmost side away from the wheel; wherein the shoulder of the body engages the shoulder of the axle positioning block so as to prevent the axle positioning block from escaping outwardly from the receptacle in a direction generally coaxial with the axle.
 2. The fork bottom of claim 1 wherein: the axle positioning block further includes an inner opening for receiving the axle at a first predetermined longitudinal position with respect to the motorcycle.
 3. The fork bottom of claim 2 further comprising: a second axle positioning block, alternatively disposable within the body's receptacle, and having a shoulder which engages the body's shoulder to prevent outward escape of the second axle positioning block; the second axle positioning block having an inner opening for receiving the axle at a second predetermined longitudinal position with respect to the motorcycle; whereby, by swapping between the two axle positioning blocks, front suspension trail geometry of the motorcycle is altered.
 4. The fork bottom of claim 1 wherein the body further includes: gusseting of an inward facing surface of the body. 